1. Field of the Invention
The subject matter of this invention is related generally to metal clad switchgear apparatus and is related more particularly to the utilization of hollow, tubular, cylindrical conductors for carrying high voltage electrical current.
2. Description of the Prior Art
Metal clad switchgear is well known in the prior art. A typical example may be found in U.S. Pat. No. 2,363,364, issued Nov. 21, 1944 to H. H. Rugg. Another example may be found in U.S. Pat. No. 2,424,345, issued July 22, 1947 to C. P. West. Typically, metal clad switchgear apparatus is utilized because of its inherent safety features. In a typical case -- a completely enclosed metal cabinet has three compartments; into one compartment, usually in the back of the cabinet, a high voltage electrical conductor is provided. In still another compartment, also usually in the back, but separated from the first compartment, a high voltage line, which is connected to a load, is provided. The load is, of course, external to the switchgear. Electrically interposed between conductors in the latter two compartments in disconnectable arrangement is circuit switching or circuit interrupting apparatus. The circuit interrupting apparatus opens or closes the circuit which exists between the conductors of the first mentioned two compartments. Furthermore, the circuit disconnecting apparatus may be physically removed from the metal clad switchgear apparatus for maintenance and repair. It has been found in the past that the terminals for the circuit interrupter apparatus operate very advantageously if they comprise radially spaced spring-loaded fingers which apply radial force to a conductor of circular cross-section. Such an arrangement is shown in U.S. Pat. No. 2,376,818, issued May 22, 1945 to M. J. Rubel. Furthermore, it has been advantageous in the past to interface the high voltage line side of the switchgear apparatus to high voltage transformers or the like by utilizing rectangularly shaped copper or aluminum bus bars. Such an arrangement is shown for example in U.S. Pat. No. 3,793,564, issued Feb. 19, 1974 to J. G. Salvati. A problem arises in connecting a rectangular bus bar with a circular conductor such as is provided for accommodating the circular fingered terminal of the previously mentioned Rubel U.S. Pat. No. 2,376,818. One way of avoiding the problem in the past has been to use only rectangularly shaped connecting means. Such an arrangement is shown in U.S. Pat. No. 3,746,817, issued July 17, 1973 to Drown et al; however, this prevents the use of the highly desirable circular finger arrangement of the Rubel patent. Furthermore, it has been found to be advantageous to use circular stud means, especially hollow cylindrical copper circular stud means, for mating with the finger arrangement of the Rubel patent for instance. The reasons for this are many. One reason lies in the fact that the relative surface area to volume of a conductor of circular cross section provides an optimum heat dissipating characteristic for the conductor. Another advantage lies in the fact that alternating current, even at the relatively low frequency of 60 Hz. follows the skin effect principle where a relatively large percentage of the current flows in the outer portion of a conductor. Consequently, the utilization of a hollow circular tubular conductor increases the efficiency of the conductor. Still another advantage lies in the fact that circular conductors by nature theoretically have no sharp discontinuities therein, such as a rectangular conductor would have, and are thus ideally suited for high voltage applications where corona is a problem. Ways of joining relatively flat rectangular conductors to circular conductors are described in various degrees in the following U.S. Pat. Nos.: 2,090,940, issued Aug. 24, 1973 to H. D'Olier; 3,303,293, issued Feb. 7, 1967 to Howel; and Re. U.S. Pat. No. 13,475, reissued Oct. 8, 1912 to Robinson. The three latter mentioned patents, although somewhat related to the interconnection of bus bars or circular conductors or the combination of both, are provided here mainly as background. On the other hand, U.S. Pat. No. 2,950,456, issued Aug. 23, 1960 to R. H. Rehdef, shows the interconnection of bus bars having right angle bends therein with circular conductors. In that case, attachment is provided by longitudinally splitting the circular conductor in a radial plane, inserting a bus bar longitudinally therein and then radially disposing bolts through the circular conductor at right angles to the broadest plane of the bus bar. This construction has a number of disadvantages, one of which lies in the relative amount of surface area of circular conductor which is available to conduct current at the interface between the circular conductor and the bus bar. Another is a potential mechanical relaxation of the circular conductor with time which would have a tendency to loosen the radially disposed bolts. Another disadvantage lies in the intricacy with which the insertion of the bus bar in the longitudinal slot and the bolting of the bus bar to the circular conductor must be accomplished. A similar disadvantage is associated with the prior art shown in FIG. 2 of the drawings of the present application in which one end of a circular conductor is threaded and the bus bar is correspondingly drilled and tapped and then rotated or revolved upon the threaded circular conductor. A separate securing operation is required thereafter for fixedly securing the bus bar in place on the threaded circular conductor for efficient current transferring therebetween.